The present invention relates to a processing-free planographic printing plate, i.e., a planographic printing plate which, after exposure, is ready for use without further processing.
Deep-etch plates and presensitized plates, as planographic printing plates, have enjoyed popularity.
Deep-etch plates are prepared by applying a light-sensitive coating to a grained aluminum or zinc plate. Upon exposure to a patterned image, the resin is hardened by exposure. The plate is then etched, removing the light-sensitive resin layer hardened by exposure. On the other hand, presensitized plates are obtained by coating a light-sensitive resin on an aluminum plate. After development, a developing ink or a protective lacquer is applied to the hardened light-sensitive resin layer which becomes the image areas. For both printing plates, a developing step is required.
The manufacture of such plates typically involves coating a metal plate with a light-sensitive resin, exposing the resin to a patterned light image and processing to selectively remove resin in the patterned shape produced by the light image.
It is this processing or etching step which is avoided in the making of processing-free planographic printing plates. Such plates, upon exposure and mounting on a printing press are immediately ready for use without any chemical processing.
"Processing-free" printing plates are disclosed, for example, in U.S. Pat. Nos. 3,650,743 and 4,115,127. These plates utilize three and two layered structures, respectively. The former includes arsenic, and the latter requires coating, by vacuum disposition, of mixed inorganic materials. Thus, both have practical disadvantages.
The general object of the present invention is to provide a practical, single layer, processing-free planographic printing plate.
A 1968 publication by R. B. Fox et al of the Naval Research Laboratory, entitled "Wettability and Constitution of Photooxidized Polystyrene And Other Amorphous Polymers" (Advanced Chemical Series, 87, 72) has reported the effect of ultraviolet (UV) irradiation in air on the wettability of thin films of amorphous polymers. Based on the polymers studied and reported upon by Fox et al, it was concluded that changes in contact angles (as an indication of wettability) for various liquids, both polar and non-polar, are a function of the nature of the polymers studied. The result obtained for the contact angle assay has been correlated with the wettability of a polymeric surface by liquids of known surface tensions. The Fox et al article details the protocol that was employed here in evaluating changes in hydrophobicity/hydrophilicity of the materials used in this invention.